EarthNotes - Tamarisk Control

Tamarisk trees grow in thick stands along the Little Colorado River near Cameron, Arizona.

John Grahame

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Flagstaff, AZ – Many land managers are combating unwanted invasive species. On the Colorado Plateau, they decided to fight one of them by introducing another new species.

The unwanted plant, in this case, is tamarisk, the thirsty plant that crowds out willows and cottonwoods along southwestern watercourses. Entomologists went to its native land - China - to find a bug that eats these brushy shrubs.

What they found was the tamarisk leaf beetle. It's a yellow-and-black, quarter-inch-long beetle that feeds exclusively on tamarisk leaves. In fact, the females mate and lay eggs only after a hearty meal, and their voracious young prefer to starve rather than switch to a different diet.

Extensive test runs showed that the newcomers do indeed appear to leave other plants alone. Beetles were finally turned loose near Moab, Utah, in 2004, and along the greenbelt of Colorado's Dolores River in 2005.

Lured by pheromones or the scent of tamarisk, and assisted by breezes, the leaf eaters spread like a juicy rumor. According to Dan Bean, director of the state insectary in Palisade, the beetles released near Moab have already stripped at least 18 river miles of tamarisk thickets.

Yet this sort of biocontrol aims at balance, not eradication. Repeated defoliation by hungry beetles doesn't wipe tamarisks out entirely - but it does stress individual plants and curtail their production of new seeds. But what will replace the tamarisks? The jury's still out. In many places active revegetation may be needed to keep other unwanted plants from moving in.